The present invention relates to a multipipe flow-dividing dilution tunnel system for dividing a gas to be inspected at a predetermined division ratio, diluting a divided gas, and sampling and testing the diluted gas for its components or constituents.
For the purpose of reducing air pollution caused by automobile emissions, it is necessary to sample automobile exhaust gases and analyze particulate materials contained in the exhaust gases and other components thereof. Total dilution tunnel systems which are used to dilute the total amount of sampled exhaust gases are large in scale and requires a large expenditure of expenses. In view of this, there has been proposed a flow-dividing dilution tunnel system which employs a small-size dilution tunnel for diluting a divided flow of exhaust gases.
FIG. 14 of the accompanying drawings illustrates a conventional flow-dividing dilution tunnel system. In the conventional flow-dividing dilution tunnel system, the exhaust gas emitted from an automobile engine is introduced into a surge tank 3 through a multipipe flow divider 2 which comprises a plurality of flow-dividing pipes 1 having the same diameter and length. The exhaust gas is thereafter discharged from the surge tank 3 through a flue 17. One of the flow-dividing tubes 1 extends out of the flow divider 2 and has a downstream end portion introduced as an inlet pipe 4 into a dilution tunnel 5. The dilution tunnel 5 has a constant-rate suction device 6 in its downstream end. The suction device 6 draws ambient air from the upstream end of the dilution tunnel 5 through a rate regulating butterfly valve 24 into the dilution tunnel 5. The divided exhaust gas which has been introduced through the inlet pipe 4 into the dilution tunnel 5 is diluted by air, or a dilution gas, from the butterfly valve 24 in a position immediately upstream of a mixing orifice 7. Fine particles of the diluted gas are passed through a corrective filter 30 and sampled by a constant-rate sampling device 31, or analyzed by an exhaust gas analyzer 32.
The flow-dividing dilution tunnel system shown in FIG. 14 can introduce a divided exhaust gas into the dilution tunnel 5 through the inlet pipe 4 at a division ratio which is equal to the ratio of the number of the inlet pipe 4 to the number of the flow-dividing pipes 1. The introduced exhaust gas is diluted by dilution air, and the diluted gas is thereafter sampled and analyzed for its constituents.
However, when the output power of the automobile engine varies, the pressure loss of the multipipe flow divider 2 also varies, resulting in fluctuations of the ratio of the amount of the divided exhaust gas which is introduced into the dilution tunnel 5 through the inlet pipe 4 to the amount of the total exhaust gas flowing into the flow divider 2. When this happens, the diluted exhaust gas cannot be accurately analyzed for its constituents. This problem may be solved when a pressure loss, equal to a variation in the pressure loss of the multipipe flow divider 2 due to a change in the total amount of the introduced exhaust gas, is given to the inlet pipe 4.